Molten plastic compositions prepared in an extruder are discharged in the form of plastic strands from a nozzle plate and are cut into granulate in a stream of a fluid, such as air or water. Due to the cutting energy imparted to the granulate, the granulate becomes heated and it is conveyed by a cooling fluid to a bath of water for separation. The speed of the granulation is controlled by the velocity of flow established for the granulates with the cooling fluid. Floating granulate, i.e. granulate of low density which collects on the surface of the cooling fluid, e.g. water readily causes the formation of lumps hereat, particularly in the case of plastics of high tackiness. With plastic products of high density, accumulations readily occur, and thus the formation of agglomerates within the system conveying the granulates and the cooling fluid.
The dwell time and thus the length of cooling of the individual granulates is dependent therefore not only on the velocity of flow of the conveyance fluid but also on the density of the individual plastic product.
In order to avoid caking of the product and to obtain an optimum granulate temperature, each plastic product furthermore requires a different residence time in the water, which, to be sure, in the case of a pipeline system which is customarily installed in fixed position and with a predetermined amount of water established thereby, can be influenced by its velocity of flow, but cannot be sufficiently determined with reference to the total quantity of granulate since the pressure flow caused by the feeding of water into the conveyance water by means of a feed pump causes turbulence.
From De-OS No. 20 45 801 there is known, for instance, a method and an apparatus for producing dry granulate from plastics in which the granulate is conducted together with the coolant within a pipeline and the extent of the removal of heat can be varied by interrupting the cooling path or optionally changing its length. With the change in the dwell time obtained thereby, the residual heat remaining in the granulate is used, primarily for the drying of the granulate itself and the guidance of the granulate in the coolant is unaffected by this.